I recently installed Office 2007, parallel to Office 2003, so they coexist :)

The thing I didn't anticipate is, that Office 2007 will bruteforce its way around.

I don't want it to open old (*.xls - excel 2003) files, just it's own, *.xlsx files.

I tried changing the default program, but it just points to excel.exe, and continues to use excel 2007, even though I clearly pointed it to use ..office\office11\excel.exe path, instead of ..\office2007\office12\excel.exe.